Adjustable thermostats



June 27, 1961 H. ENGELHARDT ADJUSTABLE THERMosTATs Filed July 16, 1959 INVZNTOR Hajo Enya! @rdf ATTORNEY dil/AM Pra'ar Arf' United States vPatent O 2,990,463 ADJUSTABLE THERMOSTATS Hugo Engelhardt, Meadowbrook, Pa., assignor to Philadelphia Thermometer Company, Philadelphia, Pa., a partnership Filed July 16, 1959, Ser. No. 827,609 9 Claims. (Cl. 200-141) This invention relates to adjustable thermostats, and primarily constitutes an improvement on the adjustable `thermostat of Patent 2,459,968, issued January 25, 1949, toJohn Leonard Schwantz.

The adjustable thermostat shown in said patent has been a successful article of commerce possessed of marked utilitjl and enhanced advantage over anything known to the prior art. While not militating against its overall success, certain attributes or characteristics of the commercial form of the patented invention have been found occasionally to be disadvantageous.

According to the said commercial form of the patented invention a double-bored column of glass terminates symmetrically at the bottom in the extreme upper end of a com-mon glass mercury bulb with both bores containing mercury in extension of mercury in the common Ibulb. One of the bores is sealed closed, in electrical communication with one circuit lead of the instrument. An adjustable wire electrode extends into the other bore and is axially adjustable therein between various predetermined temperature settings, and comprises in part the other lead of the circuit controlled by the instrument. The instantaneously set but adjustable, wire electrode, makes and breaks contacts with the mercury in its bore as the level thereof varies with variations in temperature incident on the common bulb. The double bore column at its upper end is sealed into an enlarged glass chamber or housing. The adjustable wire electrode at its upper end is connected to a guided threaded travelling or follower-nut threaded on a rotatable threaded shaft mounting a winged armature within the glass housing. The armature is rotated manually by means of an external axially fixed rotatable annular magnet. Spaced plates mount the guide for the traveling nut, and journal the shaft mounting the armature on its upper end, as a unit anchored in the glass housing above the double bored column. The remainder of the circuit lead for the movable electrode is by a wire usually connected to the upper of the plates, and the circuit is through this plate, into the threaded shaft, and into the guide for the nut and through both paths into the traveling nut, and into the axially adjustable electrode wire mounted on said nut. The unit is anchored in the glass housing by suitable indentations in the wall of the housing, or `the like.

It will be seen that the relatively moving parts are quite small and that even with close tolerances there will be variations in dimensions which result in variable contact resistances between instruments in a series. Moreover it is diicult to so locate the unit in the glass housing that the armature on the shaft is axially centered in the external annular magnet. When the armature is relatively displaced axially relatively to the center of the magnet, magnetic axial force is exerted on the armature and on the threaded shaft in one direction or the other. These factors cause varying degrees of frictional engagement between the parts and therefor introduce varying values of contact resistance into the circuit, with consequent inaccuracies and deviations in readings between various instruments in a series of successively manufactured instruments.

Furthermore, it has been frequently happened that from shocks or other causes, as in shipping, the mercury inthe adjustable wire electrode column becomes separated and discontinuous, with a gas globule or bubble diice viding the column. While this is easily corrected if the glass globule stays in the bore in which it arises, by heating 4the bulb until the bubble passes out of the upper end of this bore, it often happens that due to the symmetrical close relations of the ends of the two bores of the column in acorrunon pocket at the top of the common bulb, the gas globule moves through the mercury, out of the open bore in which it occurs, and enters the closed bore. When this occurs this column becomes broken and affects current transmission. This is a more serious matter as it involves return to the factory, and expensive dismantlement to remove the break in the closed column of mercury. While this may be and usually is an infrequent occurrence, it is always a potential, and is a disadvantage of the thermostat.

`It is among the objects of this invention: to improve adjustable thermostats; to minimize the contact resistance `and make it substantially uniform in any series of adjustable thermostats; to provide a shunt circuit in one lead of an instrument circuit to minimize contact resistance therein; to provide an adjustable thermostat of the double bored colurrm type merging into a mercury bulb with means substantially precluding movement of a gas globule or bubble from one bore through the mercury in the bulb and into the other bore; and many other objects and advantages will become more apparent as the description proceeds. p

In the accompanying drawings forming part of this description: i A

FIG. l'repersents a fragmentary longitudinal section through the Ithermostat of this invention, but with mercury omitted, except toward the bottom of the bulb, for clarity.

FIG. 2 represents a transverse section taken on line 2-2 of FIG. l, with the constricted portions of the lower part of the instrument omitted, for clarity.

FIG. 3 represents a transverse section taken on line 3-3 of FIG. l, with the lower plate and the constricted portions of the lower part of the instrument omitted, for clarity. v

FIG. 4 represents a fragmentary section, partially yin elevation and partially broken away, of the lower end of the instrument according .to this invention, with mercury omitted, for clarity.

FIG. 5 represents a fragmentary Vertical section through the traveling nut, the threaded shaft and the guide for the nut, showing one application of a shunting conducting spring engaging the guide and the nut to reduce contact resistance.

FIG. 6 represents a transverse section taken just below the nut in FIG. 5.

FIG. 7 represents a view similar to that of FIG. 5, but with the shunting conducting spring engaging the nut and the threaded shaft toy reduce contact resistance.

FIG. 8 represents a transverse section taken through FIG. 7 just below the nut in FIG. 7.

FIG. 9 represents a fragmentary vertical section through the mergence of the double-bored column and the bulb, according Ito prior art practices, with the mercury removed for clarity, and showing diagrammatically a gas globule leaving one bore, and in dotted lines indicating its transfer into the closed bore, which this invention precludes.

Referring to FIG. l, a glass envelope or housing 10 is provided having a constricted closed upper end 11, and merging at its lower end into the upper end of a glass double-bored column 12. The column 12 contains a closed bore 13 and an open bore 14. The lower end of the double bore column 12 is sealed in attachment to 'a common mercury bulb 15. It will be understood that the glass envelope 10, as in said Schwartz patent, is charged with inert gas under pressure, and the thermostat constitutes a pressure loaded instrument. The instrument, toward its upper end externally mounts a rotatable annular magnet 19. Within the housing is the control unit. This is comprised' of a lower `plate 16, anchored in the housing by any suitable means, as is common, having a suitable recess (not shown) to permit the non-contacting passage of an electrode wire, to be described, at one end of the control unit, and an upper plate 17, at the other end of the unit. The plate 17 may also be anchored to the housing 10. The recited plates 16 and 17 in spaced relation mount an insulating glass tube 18, and a separate metal guide rod 20, or like guiding element, and journal the threaded shaft 21. The upper end of shaft 21 above plate 17 mounts the winged armature 22, in general axial and radial juxtaposition to the external magnet 19. The foregoing is substantially as shown in said patent. A traveling or follower nut 23 is threaded on shaft 21, and, illustratively, has a bifurcated edge 24, slidably engaging on and guided by the metal rod 20. One lead wire 25 of the control circuit of the instrument extends from a terminal 26 in the upper end of the instrument, through insulating glass or like tube 18, into the upper end of closed bore 13 in the column 12, to termination in contact with a mercury column in the lower portion of bore 13. The wire 25 is anchored and the bore 13 is closed by the sealing block 27 fused to the wire above its lower terminus in the mercury column of bore 13 below the block. It will be seen that a break in the mercury column of the lower end of bore 13, as by a gas globule, would interfere with current transmission from wire 25 into or from the mercury in the bulb 15. The other lead wire of the instrument circuit is comprised in first part by wire 28, extending from a terminal 30 in the upper end of the instrument, to electrical engagement with upper plate 17. The second part of the other circuit lead comprises a wire electrode 31, electrically connected at its upper end to the traveling nut 23, extending out of contact past the lower plate 16, and at its lower end extending `into the mercury bore 14, of the double bored column 12. The circuit is completed between wire 28 and electrode wire 31 across plate 17 into shaft 21 and into the traveling nut 23 and also through guide rod 20 into the traveling nut 23. Preferably the electrode wire 31 is formed according to the teachings of Patent 2,421,292, issued to John Leonard Schwartz on May 27, 1947, for accurate centering of the electrode in the bore 14.

The lower end of the column 12 is axially drawn and reduced in diameter, in a lower terminal portion 32, having a generally fiat end surface 33, containing the opening of the closed bore 13, and if desired also containing the lower end of the open bore 14. Preferably, however, the lower terminus 32 of the column 12 fuses shut the lower end of the bore 114. 'Ihe bore 14, at a point spaced from the end 33 of the reduced portion 32 is enlarged laterally into a recess or lateral aperture in the side surface of the reduced portion 32, as at 34. The thin walled common bulb envelope is upwardly convergent and is fused to the column 12 just above the aperture 34.

In order to stabilize the contact resistance and to render it as nearly uniform and of as low a value as possible, `in a series of the instruments, a resilient shunting coil 37 of conducting material is provided with its upper end anchored in electrical connection to the traveling nut 23, `and vbearing slidably against, or embracing, either the metal guide rod 20, or the threaded shaft 21. As, owing to the relatively weak magnetic coupling between the rotatable annular magnet 19, and the armature 22, due in part to radial spacing, the friction in the system must be kept low, it is preferred to form the coil 37 of slightly larger diameter than that of either the rod or ythe threaded shank 21, and to make the axes of the spring l37 and the engaged element eccentric, so :that the ywiping vcontact betweenthe springend the rod Vor threaded shank is'against one side only thereof.r In FIGS. 1, 3, 5-and 6,

the spring 37 is shown engaging the guide rod 20. In FIGS. 7 and 8 the spring 37 is shown engaging the threaded shank 21. Of course two such springs can be used, one for each of the rod and the shaft, but generally this is redundant and imposes too high a frictional resistance. In any case, regardless of whatever contact resistance may exist or develop between the shaft 21 and/ or the guide 20 and nut 23, the shunting spring contact 37 obviates same and establishes a direct path of minimal contact resistance between the plate 16 and nut 23.

It will be seen that by the auxiliary shunt electrical path established between the plate 17 and the traveling nut 23 the contact resistance therebetween is minimized, with enhanced accuracy and uniformity.

It has been mentioned that a globule of gas entering closed bore 13 is ditiicult to remove, whereas in open bore v14 it is a simple task, requiring only heating of the bulb 15 until the mercury column 14 rises into the lower end of the housing 10, and that preclusion of the entry of such globule into bore 13 is a primary object of the invention. FIG. 9 shows a fragmentary section of the schematic joinder of the lower end of a double bored colyumn 12' with the common bulb 15', according to the prior art, with the end of a closed bore 13 of column 12 in immediate juxtaposition to the end of an open bore 14 of said column at the upper end of the bulb 15. It will be understood that in the event of a break in the mercury column of bore 14', a gas globule 8 therein can enter the bulb for any reason, such as manipulations or reduction of temperature, and, being confined in a pocket at the inner top of the bulb can pass readily across the barrier 7 between the ends of the respective bores, or can move circumferentially about the upper inner end of the bulb and into bore 13'. This is because the openings of both tubes are adjacent to each other in the pocket formed by the inner surface of bulb 15 at its jointure with the column 12.

It will be seen that such bubble or globule transfer'is for all practical purposes impossible with the structure of FIG. l. The end 32 extends well into the bulb remote from the pocket formed by the inner surface of the upper end of the bulb l15, and the aperture 34 is the only bore opening into such pocket. Any gas globule formed in bore 14 can pass out through the enlarged end 34 thereof in the upper part of the bulb. Rotation or other manipulation of the instrument finds it possible only for the gas globule to pass back into bore 14, from which, as noted, its removal is simple. It cannot move through the body of mercury to the entrance of bore 13 in the face 33 of the terminal end of the elongated drawn out end 32. In passing it may be noted that a desired function of the attenuated end 32 of the column is to minimize the displacement of mercury in the bulb and therefor to keep the volumetric size of the bulb to a minimum. Where this is not significant the column of uniform diameter may be provided with the lateral aperture 34 leading into bore 14, spaced from the end of the column with the remainder of the bore 14 closed or open, and with the bulb envelope sealed to the column just above the orifice. ln any case the desired construction finds the aperture 34 axially spaced above the end of bore 13 in the bulb 15.

I claim as my invention:

l. In a pressure loaded instrument having a double bored collunn leading into a common mercury bulb, sealed to said column in a general line of mergence, of which one of said bores is axially closed and the other of which is axially open to receive an adjustable wire electrode, said column extending into said bulb beyond said general line of mergence to effect an orifice for the closed bore within said bulb, `and aperture means formed in said column into the said open bore within said bulb adjacent to and internally of the general line of mergence thereof with said bulb, and spaced axially lof the column from said orifice within the-bulb.

2. A pressure loaded instrument comprising a column of glass having two spaced parallel bores, a bulb envelope sealed to said column in spaced relation to the end thereof, a lateral enlargement of one only of said bores prow'ding a lateral recess in said column adjacent to the jointure of said envelope and within said envelope.

3. A pressure loaded instrument of the class described comprising a glass column 'having two spaced parallel bores, a glass bulb envelope sealed to the column at a general peripheral line in spaced relation to the end of said column whereby one bore at least extends into the bulb in spaced relation to the said general line of jointure of the bulb and the column, said column having a lateral recess inwardly of the bulb but -substantial adjacent to said general line leading into the other of said bores in spaced relation axially of the column to the termination of said one bore in the end of said column within said bulb, whereby any gas bubble passing out of said lateral recess is conned within the bulb adjacent to said general line out of ycontact with the end of said one bore.

4. A pressure loaded instrument as in claim 3, -irr which the end of the column in said bulb is tapered.

5. A pressure lloaded instrument of the class described comprising a glass column having. parallel spaced bores, a wire electrode extending into one of said bores, means supporting said electrode for adjustable positioning therein comprising a traveling nut, a threaded shaft engaging said nut and forming together an electrical path, an armature on said shaft, an annular magnet adjacent to said armature, and shunt means for electrically connecting said traveling nut and said shaft with minimal Contact resistance.

6. A pressure loaded instrument of the class described comprising a glass column having a bore, a mercury bulb communicating with said bore, -a wire electrode in said bore, means for axially adjusting said electrode in said bore comprising a unit in general axial alignment with said column comprising a plate, a threaded shaft journaled in said plate, means for rotating said shaft, a traveling nut threaded on said shaft, said wire electrode con.-

nected to said nut, means connected to said plate cornprising a guide for said nut, means connecting said plate to a circuit lead and forming with said shaft and said nut an electrical path, and means in electrical connection with said plate for establishing a shunt circuit between said plate and said nut of relatively low contact resistance.

7. A pressure loaded instrument of the class described comprising a glass column having a bore, a mercury bulb communicating with said bore, a housing fused to said column, an actuating unit in said housing comprising a conducting plate, a pair of contact members connected to said plate one of which comprises a threaded shaft journalled in said plate and the other of which comprises a metallic guide element, means for rotating said threaded shaft, a traveling nut threaded on said threaded shaft and bearing against said guide element, a wire electrode mounted on the traveling nut and extending axially into said bore, conductor means for one lead of a circuit connected to said plate and forming with said contact members and said nut an electrical path, and shunting means engaging said traveling nut and one of said contact members for conducting current therethrough with minimal Contact resistance.

8. A pressure loaded instrument as in claim 7, in which both of said contact members are substantially cylindrical and said shunting means comprises a coiled spring surrounding a contact member.

9. A pressure loaded instrument as in claim 8, in which the spring is of greater diameter than the contact member and engages same eccentrically.

References Cited in the le of this patent UNITED STATES PATENTS 999,710 Freas Aug. l, 1911 2,459,968 Schwartz Ian. 25, 1949 2,536,089 Ratchford et al Jan. 2, 1951 FOREIGN PATENTS 181,004 Germany n- Dec. 31, 1906 600,960 Germany Aug. 4, 1934 

